Low cost has made ATA (Advanced Technology Attachment) disk drives a popular choice for data storage in various data processing systems. The development of the Serial ATA (SATA) protocol has furthered this popularity by providing features such as hot-pluggability, flexible cabling, and CRC (cyclic redundancy check) for all data, command, and status communications. In addition, the storage density of ATA disk drives makes them particularly advantageous for large-capacity storage systems. Accordingly, Redundant Array of Independent Disks (RAID) implementations, which have traditionally employed SCSI or Fibre Channel disk drive technologies, are currently adopting the use of ATA disk drives.
Current ATA disk drives, however, only support a standard-sized sector format of 512 bytes, whereas applications or other software that interact with the disk drives, such as a RAID implementation, can require sectors of a different size. A sector is the smallest unit for which an access can be made to the disk. The difference in sector size requires address translation between the addresses and sectors specified by an application, referred to as logical addresses and logical sectors, and the physical addresses and physical sectors of the disk drive. This sector-size difference also produces a misalignment between logical and physical sectors of the disk drives. For example, if a logical sector is larger (in bytes) than a physical sector, then the logical sector overlaps multiple physical sectors. Consequently, a write operation to a logical sector is, in effect, a write operation to multiple physical sectors, although portions of one or of all of these physical sectors are not being written to. These portions are located at the edges of the overlap between the logical sector and the physical sectors; such edges are referred to as sector edges. This write operation can require an additional read I/O operation to obtain data from the sector edges. Additional read I/O operations of sector edges thus have performance implications for applications that perform small write or large misaligned write operations.
U.S. Pat. No. 7,277,986 issued to Morley, et al. on Oct. 2, 2007 entitled “Sector-edge cache” describes a sector-edge cache that stores sector edges obtained from sectors during previously executed read and write operations.